The single crystalline form of an insulator, ${\mathrm{Sr}}_3{\mathrm{CuIrO}}_{6+\delta }$, is shown to exhibit unexpectedly more than one magnetic transition (at 5 and 19 K) with spin-glass-like magnetic susceptibility behavior. On the basis of this finding, viz., inhomogeneous magnetism in a chemically homogeneous material, we propose that the idea of “phase separation” described for manganites is more widespread in different ways. The observed experimental features enable us to make a comparison with the predictions of a recent toy model on magnetic phase separation in an insulating environment.

• Received 12 July 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.107202